A vehicle occupant restraint apparatus comprises a restraint, such as an air bag, and an inflator for providing a gas for inflating the restraint. The inflator contains an ignitable gas generating material which, when ignited, generates the gas. The gas generating material is contained within a combustion chamber.
An actuator or squib is customarily located at one end of the combustion chamber. In the event of a collision, pyrotechnic material in the actuator or squib is ignited. This burning pyrotechnic material is forcibly ejected into the combustion chamber to ignite a substantial amount of the gas generating material at one end of the combustion chamber.
The ignition of the pyrotechnic material in the actuator or squib and the subsequent ignition of the gas generating material can create shock waves which travel the length of the combustion chamber. The inflator commonly has one or more filters between the combustion chamber and the air bag. These filters are positioned in the flow path for the gas which is generated in the combustion chamber. The shock waves which are generated can subject the filters to almost instantaneous and substantial stresses.
U.S. Pat. No. 5,345,875 discloses a gas generator with means to attenuate a shock wave. The generator comprises a propellant container containing a plurality of propellant grains and an igniter for igniting the propellant grains. A shock wave barrier in the form of an apertured plate is positioned in the propellant container close to the igniter. The barrier attenuates the shock waves emanating from the igniter. The object of the barrier is to prevent fragmentation of the propellant grains.